Most of us are familiar with the energy drain that sets in around 2:00 p.m. or so. Whether you call it a lunch coma or the midday blues, it’s a brain zapping dullness that leaves you staring blankly at your monitor and thinking an afternoon run to Starbucks might not be a bad idea.
First, it helps to understand what is meant by “rewards” in this context. You could say our reason for getting up in the morning, going to work, taking on the challenges of the day, and everything else we do is all about rewards – what we seek to accomplish, earn, learn, achieve, influence, etc. The brain is structured to focus on rewards of all sorts, almost all the time. But as this study shows, the time pattern of reward seeking ebbs and flows as the day unfolds.
The researchers used fMRI to scan the brains of a small group of volunteers at three points during the day (10 a.m., 2 p.m., and 7 p.m.), focusing on their brains’ reward systems. They found that activation in a brain area called the left putamen was highest early and late in the day and lowest in the early afternoon. The left putamen plays a big role in the processing and expectation of rewards, and this study reveals that its mojo peaks in the morning and early evening and dips around 2 p.m.
The researchers think what’s happening is the brain experiences a “prediction error” about when to expect rewards. The lowest expectation is early and late in the day, so energy to seek out rewards is higher. (One way to look at this is if you don’t expect something is coming, you expend more energy to get it.) Reward expectation peaks around midday, hence the slog. The upside is that prediction error periods serve an important purpose: We tend to learn and accomplish more during those times because of the misalignment of expectations and rewards—just one of the many paradoxes embodied in our noggins.
That explanation is speculative at this point, but the feeling is certainly familiar. Add a drop in blood sugar after a big lunch and a caffeine crash after three cups of coffee in the morning, and it’s easy to see why midday isn’t the best time to dive into that big project you really need to ace.
The study was published in the Journal of Neuroscience.